The theory of the optimal detection of sudden anomalies of VLF-signal phase on ionospheric paths

It is shown that, during the detection of infrequent exponential pulses on a background of normal noise, the optimal threshold is the level corresponding to a third of the mean-square deviation of the noise. For the example considered, the mean-square deviation of VLF-signal phase in the ionosphere amounts to 5-10 deg when sudden phase anomalies determined by solar effects are observed. Hence, the optimal threshold for the detection of sudden phase anomalies amounts to 2-3 deg.